This invention relates to measuring and testing and more particularly to an improved instrument for quickly and accurately measuring the softening temperature of glass and similar products.
In working with glass, it is often desirable to know the softening temperature of the glass. For example, a number of different colored glasses are commonly used in decorative or art glass, such as paperweights. If the different glass compositions used in a product have substantially different softening temperatures, it may be difficult or impossible to combine these compositions. In forming paperweights, for example, bits of glass having different colors may be adhered to the surface of a heated gob of clear glass. The gob of glass with the attached bits then is reheated until the bits of glass are sufficiently plastic to permit working into a desired design. After the design is formed, the paperweight is finished by adding an outer layer of clear glass, in a conventional manner. If the bits of colored glass should have an appreciably higher softening temperature than the gob of clear glass, the colored glass cannot be worked into a desired pattern without overheating the clear glass. In the manufacture of other products from glass, it also may be desirable or necessary to know the softening temperature of the glass. This is particularly true in research where new glass compositions are developed.
According to the prior art, it has been very difficult and time consuming for measuring the softening temperature of thermoplastic materials such as glass. The normal prior art method for measuring the softening temperature of a glass involves suspending the upper end of a uniform fiber formed from a specimen of the glass within a furnace. The fiber extends below the furnace into a chamber having a transparent window. A technician observes the lower end of the fiber through the window and the temperature within the furnace as the temperature is gradually increased. When the upper end of the fiber is heated to its softening temperature, the fiber will begin to elongate. When the fiber elongates at a predetermined rate, the technician records the temperature within the oven. A test of this type may take several hours and requires the presence of a technician to observe the fiber as it is heated to its softening temperature. As a consequence, the test is expensive to run. In addition, the specimens must be uniform both in diameter and in roundness over its entire length and must have a diameter falling within narrow range. Otherwise, the indicated softening temperature will be inaccurate.